How to Calculate the Electric Circuit Load of a Sub Panel

Application: Installing a Circuit to a Garage Sub Panel.
Skill Level: Intermediate to Advanced – Best installed by a Licensed Electrical Contractor.
Tools Required: Basic Electricians Pouch Hand Tools, electric drill, auger bits and extension cord.
Estimated Time: Depends on personal level experience, ability to work with tools and install electrical circuit wiring.
Precaution: Identify the panel power source, turn it OFF and Tag it with a Note before working with the new circuit wiring.
Notice: Installing additional circuits and electrical wiring should be done according to local and national electrical codes with a permit and be inspected.

Understanding the Circuit Capacity of a Garage Sub Panel

In order to add a circuit to your garage sub panel that would provide power to a sub-panel for your shed one would first need to know the amperage size of the garage sub panel.

Determine the proposed electrical circuit loads that will be installed in the shed.

Will these new circuit be 120 volts only or will there be any 240 volt circuits, and what will the amperage load of these circuits actually be so the size of the sub-panel can be determined for the shed.

The existing 15 amp and 20 amp circuit loads which are being supplied by the garage sub panel must be evaluated to determine the actual amount of amperage load that is being placed on the garage sub panel.

Once all this electrical load information is obtained and calculated then it could be determined if the garage sub-panel actually can handle the additional load for the proposed shed sub-panel and the additional electrical loads.

More about Electrical Wiring for a Sub Panel

Sub-Panel Electrical Wiring for the Home

Electrical Sub-Panel wiring considerations for the home complete with pictures. Careful planning for your Sub-Panel with immediate and future load considerations will help you understand how to size your Sub-Panel. This information will help as you consider a Sub-Panel and its size.

Electrical Wire for the Home

Garage Electrical Wiring

Garage electrical wiring diagram and considerations for wiring garage circuits, complete with pictures. Careful planning for your garage with immediate and future equipment considerations will help you understand how to size your electrical circuit requirements. This information will help as an garage electrical wiring guide.

If I understand the question correctly, this would be a sub sub panel from a sub panel fed from a main panel. The capacity of the entire system needs to be evaluated. The following is a quote from your sub panel link:

“Important Factor: Find out if the Main Service or the Panel that will supply the Sub-Panel Circuit have adequate Load Capacity and space for the needed circuit breaker.”

That is correct Forrest, the loads of the entire electrical system must be evaluated to understand if there is ample capacity for the proposed load to be added.
Thanks for sharing your comment about adding a panel,
Dave

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